Wear resistant compacts or elements comprising polycrystalline diamond are utilized for a variety of uses and in a corresponding variety of mechanical systems. For example, wear resistant elements are used in drilling tools, machining equipment, bearing apparatuses, wire drawing machinery, and in other mechanical systems. For example, it has been known in the art for many years that polycrystalline diamond (“PDC”) compacts, when used as cutters, perform well on drag bits. A PDC cutter typically has a diamond layer or table formed under high temperature and pressure conditions and bonded to a substrate (such as cemented tungsten carbide) containing a metal binder or catalyst such as cobalt. The substrate may be brazed or otherwise joined to an attachment member such as a stud or to a cylindrical backing element to enhance its affixation to the bit face. The cutting element may be mounted to a drill bit either by press-fitting or otherwise locking the stud into a receptacle on a steel-body drag bit, or by brazing the cutter substrate (with or without cylindrical backing) directly into a preformed pocket, socket or other receptacle on the face of a bit body, as on a matrix-type bit formed of tungsten carbide particles cast in a solidified, usually copper-based, binder as known in the art. Thus, polycrystalline diamond compacts or inserts or cutting elements often form at least a portion of a cutting structure of a subterranean drilling or boring tools; including drill bits (e.g., fixed cutter drill bits, roller cone drill bits, etc.) reamers, and stabilizers. Such tools, as known in the art, may be used in exploration and production relative to the oil and gas industry. A variety of polycrystalline diamond compacts and inserts are known in the art.
A PDC typically includes a diamond layer or table formed by a sintering process employing high temperature and high pressure conditions that causes the diamond table to become bonded or affixed to a substrate (such as cemented tungsten carbide substrate). More particularly, a PDC is normally fabricated by placing a cemented carbide substrate into a container or cartridge with a layer of diamond crystals or grains positioned adjacent one surface of the substrate. A number of such cartridges may be typically loaded into an ultra-high pressure press. The substrates and adjacent diamond crystal layers are then sintered under ultra-high temperature and ultra-high pressure (“HPHT”) conditions. The HPHT conditions cause the diamond crystals or grains to bond to one another to form polycrystalline diamond. In addition, as known in the art, a catalyst may be employed for facilitating formation of polycrystalline diamond. In one example, a so-called “solvent catalyst” may be employed for facilitating the formation of polycrystalline diamond. For example, cobalt, nickel, and iron are among solvent catalysts for forming polycrystalline diamond. In one configuration, during sintering, solvent catalyst comprising the substrate body (e.g., cobalt from a cobalt-cemented tungsten carbide substrate) becomes liquid and sweeps from the region adjacent to the diamond powder and into the diamond grains. Of course, a solvent catalyst may be mixed with the diamond powder prior to sintering, if desired. Also, as known in the art, such a solvent catalyst may dissolve carbon. Such carbon may be dissolved from the diamond grains or portions of the diamond grains that graphitize due to the high temperatures of sintering. The solubility of the stable diamond phase in the solvent catalyst is lower than that of the metastable graphite under high-pressure, high temperature (“HPHT”) conditions. As a result of this solubility difference, the undersaturated graphite tends to dissolve into solution; and the supersaturated diamond tends to deposit onto existing nuclei to form diamond-to-diamond bonds. Thus, diamond grains become mutually bonded to form a polycrystalline diamond table upon the substrate. The solvent catalyst may remain in the polycrystalline diamond layer within the interstitial pores between the diamond grains or the solvent catalyst may be at least partially removed from the polycrystalline diamond, as known in the art. For instance, the solvent catalyst may be at least partially removed from the polycrystalline diamond by acid leaching. A conventional processes for forming polycrystalline diamond cutters is disclosed in U.S. Pat. No. 3,745,623 to Wentorf, Jr. et al., the disclosure of which is incorporated herein, in its entirety, by this reference. Optionally, another material may replace the solvent catalyst that has been at least partially removed from the polycrystalline diamond.
Thus, during the HPHT sintering process, a skeleton or matrix of diamond is formed through diamond-to-diamond bonding between adjacent diamond particles. Further, relatively small pore spaces or interstitial spaces may be formed within the diamond structure, which may be filled with the solvent catalyst. Because the solvent catalyst exhibits a much higher thermal expansion coefficient than the diamond structure, the presence of such solvent catalyst within the diamond structure is believed to be a factor leading to premature thermal mechanical damage. Accordingly, as the PCD reaches temperatures exceeding about 400° Celsius, the differences in thermal expansion coefficients between the diamond and the solvent catalyst may cause diamond bonds to fail. Of course, as the temperature increases, such thermal mechanical damage may be increased. In addition, as the temperature of the PCD layer approaches 750° Celsius, a different thermal mechanical damage mechanism may initiate. At approximately 750° Celsius or greater, the solvent catalyst may chemically react with the diamond causing graphitization of the diamond. This phenomenon may be termed “back conversion,” meaning conversion of diamond to graphite. Such conversion from diamond to graphite may cause dramatic loss of wear resistance in a polycrystalline diamond compact and may rapidly lead to insert failure.
Thus, it would be advantageous to provide systems for transferring heat from a cutting element or wear element comprising polycrystalline diamond during use. In addition, it would be advantageous to provide a subterranean drill bit and/or apparatuses for use therewith that may cool or otherwise transfer heat from at least a portion of the subterranean drill bit.